Simultaneous in vivo measurement of lumped constant and rate constants in experimental cerebral ischemia using F-18 FDG.

Lumped and transfer rate constants in ischemic brain tissue must be measured to estimate accurately cerebral glucose utilization by the deoxyglucose method. We studied the bilateral middle cerebral artery occlusion model in 17 cats, 5 with a 1-hour occlusion, 5 with a 4-hour occlusion, and 7 with a sham operation. The time course of cerebral tissue radioactivity (Ci*(t)) was monitored by external coincidence counting during a programmed infusion of [18F]-2-deoxy-2-fluoro-d-glucose (18F-2-FDG). Arterial plasma concentration (Cp*(t)) of the tracer was kept constant during the first 45 minutes. Rate constants were estimated from Ci*(t) and Cp*(t) by a nonlinear least-squares fitting routine. The lumped constant was estimated from the fit of the ratio of extraction fractions of glucose and 18F-2-FDG by nonweighted, nonlinear least-squares fitting. In the 4-hour-occlusion model, the transfer constant k1* was 23% lower, k3* 39% lower, and the lumped constant 78% higher than in the sham-operated animals. In the 1-hour-occlusion model, k3* was 26% lower than in the sham-operated animals but the lumped constant was not significantly different. The rate of glucose utilization was significantly different in the 4-hour-occlusion model compared to the sham-operated animals (48% decrease, p less than 0.05) but was not significantly different in the 1-hour-occlusion model.